mm: use pgoff in struct vm_fault instead of passing it separately

struct vm_fault has already pgoff entry.  Use it instead of passing
pgoff as a separate argument and then assigning it later.

Link: http://lkml.kernel.org/r/1479460644-25076-4-git-send-email-jack@suse.cz


Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>